This invention relates to x-ray imaging equipment for obtaining transmitted images of soft human tissue, especially from the breast area.
It is generally believed that early detection of cancer is necessary in order to enhance a patient's chances of recovery. It is anticipated that mammary carcinoma (or breast cancer) will soon be ranked at the highest cause of death among females in certain countries. It is therefore necessary to conduct mass-screening of females in these high risk areas so that mammary (or simply breast) cancer can be detected as early as possible.
Although palpation has been the major method for detecting breast cancer, a technique has been developed in which radiation having a high x-ray absorption coefficient on soft tissue such as the breast is used to produce x-ray images on film. However, since the aforementioned soft radiation has high absorption attenuation by breast tissue, the radiation methods pose certain problems. The amount of radiation required to obtain a clear image by a film photographing technique may be relatively high and accordingly, the risk to patients receiving high radiation dosages may be correspondingly high.
In order to reduce the effects of absorption attenuation, radiation at shorter wavelengths, that is, wavelengths shorter than soft x-rays, is used in some radiography processes. This short wavelength radiation however, will penetrate all types of tissues and it is therefore difficult to discern diseased tissue from healthy tissue in an x-ray picture. The term soft x-rays or soft x-ray radiation as herein used shall refer to x-ray radiation that is at wavelengths capable of producing an image in which diseased or cancerous tissue can be defined and at low enough levels where it will not damage healthy tissues during the exposure period.